The patent of Burack et at., U.S. Pat. No. 5,259,051, granted Nov. 2, 1993, hereby incorporated by reference herein, describes a method for making optical backplanes by using a robotic routing machine to apply optical fibers to a fiat surface of a flexible plastic substrate. The fibers are bonded to the substrate by a pressure-sensitive adhesive, and after routing they are covered by a plastic sheet that encapsulates them to protect them, to give structural mechanical stability, and to keep the optical fibers in place during the handling of the optical backplane. The component optical fibers are typically used as large-capacity transmission lines between printed wiring boards or between optical circuits.
The copending application of Burack et al., Ser. No. 07/1954,720, filed Sep. 30, 1992, describes the difficulty of applying the plastic sheet to the optical fibers in a manner that gives the attributes of a good encapsulation but without damaging the fibers. A two step process is described for applying heat and pressure with platen press apparatus. While we have found that this method of encapsulating the fibers gives greatly improved results, we have found that too often fibers are nevertheless damaged; in an effort to avoid all damage, the stability and dependability of the encapsulation is sometimes compromised. These problems occur particularly when an extremely dense array of optical fibers including many crossovers is included on the surface of the flexible plastic substrate. Accordingly, it would be deskable to provide an encapsulation method that firmly encases optical fibers, including optical fiber crossovers, without damaging or weakening any of the fibers.